Methods are known for the start-up of the electric motor via a drive circuit. To this end, the electric motor is connected to a voltage source via a drive circuit, wherein the operating switch is arranged between the drive circuit and the voltage source. The operating switch switches the supply voltage on the drive circuit, which then starts up the connected electric motor.
If the operating switch is open, the electric motor runs down. During the run-down of the motor, as a result of the generative motor voltage of the decelerating electric motor, a voltage is still present on the drive circuit. Even once the electric motor is at rest, a voltage will continue to be present on the drive electronics for a further 1-2 seconds, as a result of the existing capacitances of electronic components. Only upon the undershoot of a minimum supply voltage of for example 5 V will the electronics switch over to a state in which they can only resume operation via a reset, immediately a sufficient supply voltage for the electronics is restored.
In order to ensure the trouble-free operation of the electric motor, the electronics in the drive circuit must detect the state of the operating switch. As the voltage present on the drive circuit, resulting from the generative motor voltage during the run-down of the electric motor, is such that the clear detection of a closed operating switch cannot be guaranteed, an additional contact on the operating switch is generally employed for this purpose. Via this additional contact, the drive circuit receives information on the switching state of the operating switch.
For the switch-in of an electric motor via a drive circuit, operating switches with an additional contact for the detection of the switching state of the operating switch are generally required which are structurally complex, and thus cost-intensive. In the event of the failure of the additional contact for the detection of the switching state of the operating switch, the correct operation of the electric motor cannot be guaranteed.